Extinct Sea Creatures Got the Bends

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Marine reptiles that cruised the planet's oceans millions of
years ago may have suffered from their own version of the bends,
studies of their fossils suggest. But scientists are in
disagreement over why this happened.

Human divers today get
the bends, or decompression sickness, when they surface too
quickly from the high-pressure environment of deep water.
Nitrogen bubbles form in the body and can cause immediate
symptoms like joint pain and headaches. But the bends can also
leave permanent scars, in the form of bone lesions from a disease
called dysbaric osteonecrosis, or DON.

The same type of lesions can be found in the fossilized remains
of some ancient animals, including
ichthyosaurs, giant dolphin-shaped reptiles that lived
between 245 million and 90 million years ago, researchers led by
Bruce M. Rothschild, of the University of Kansas, documented in a
paper earlier this year in the journal Naturwissenschaften.

But in the fossil record, these scars are absent from early
ichthyosaurs of the Triassic period. The bone deformities only
show up later, in the Late Jurassic through Cretaceous periods,
after new, fast predators entered the scene. Fleeing from these
predators — in particular, sharks — might have forced
ichthyosaurs to make emergency trips to the surface, causing the
bends, the researchers said. [ Into
the Blue: The Ocean's Deepest Divers (Infographic) ]

Another researcher, John Hayman, of the University of Melbourne,
has offered a different opinion. Hayman interprets these scars
differently. Rather than from rapid surfacing, the marine
reptiles, he suggests, might have gotten the bends if herded into
and trapped in shallow water by predators, he wrote in a
commentary in Naturwissenschaften.

Or, he said, after the reptiles evolved the ability to dive
deeper and for longer stints of time, air inhaled at the ocean's
surface would be pressurized due to compression of the rib cage
at depth causing excess nitrogen to be dissolved in the body.
Then, when resting at the surface, that excess nitrogen would
come out of solution and possibly form intravenous bubbles,
Hayman explained.

Hayman and Rothschild seem to at least agree that the bends were
bad for the ichthyosaurs and might have contributed to their
demise.

While whales and dolphins developed systems that permitted them
to excrete excess nitrogen and
avoid decompression sickness, ichthyosaurs seem to have
become extinct before doing the same. The bends probably caused
painful symptoms for the reptiles, the researchers say, and
impaired their ability to find food and flee predators.